The present invention relates to a damper system, and more particularly to a mechanical lead/lag damper system for a rotor system of a rotary wing aircraft.
Rotary-wing aircraft include lead/lag dampers to increase rotor blade lead/lag mode damping characteristics. The damper assembly reacts against lead/lag motions of each rotor blade assembly of the rotor system to dampen harmonic oscillations due to the lead-lag motion of the rotor blades.
The lead-lag motion of the rotor blades is primarily described by two frequencies, 1P motion and approximately 1/3P motion (once per revolution and once per three revolutions, respectively). The 1P motion, although the largest in amplitude, does not typically require damping as the 1P motion remains substantially stable. The 1/3P motion (e.g., regressive lag mode) is typically a relatively small amplitude, but may become unstable if undampened and excited by certain flight conditions and ground resonances of the rotary-wing aircraft.
A single lead/lag damper on each blade suppresses the 1/3P motion but needs to also endure the 1P motion such that the lead/lag damper may provide some damping of the 1P motion—even though none is required. To provide ample damping of the 1/3P motion and endure the 1P motion, the damper has to be oversized, primarily because of the 1P motion.
Although effective, current lead/lag dampers operate under high pressures and require a relatively long stroke which may require relatively comprehensive maintenance attention. As each rotor blade requires a lead/lag damper, the dampers may increase the overall structural envelope and weight of the rotor system.